Vapor pressures of osmium, rhodium, and ruthenium carbonyls

Abstract

Vapor pressures of solid Os3(CO)12, Rh6(CO)16, and Ru3(CO)12 were determined by the gravimetric torsion effusion method. The vapor pressures of Os3(CO)12 ranged from 10−6 to 10−3 kPa at 349 to 396 K. There was virtually no decomposition of the Os3(CO)12, and the measured molecular weight was nearly the same as that of the actual value of 906.7 g/mol. The vaporization studies of Rh6(CO)16 showed that it decomposed to Rh metal between 325 and 365 K. The measured molecular weight of the effusing gas from the solid Rh6(CO)16 was 27.75 g/mol, close to that of carbon monoxide compared to the values expected in absence of decomposition of 1065.56 g/mol. The Ru3(CO)12 vaporization was complex as there was partial decomposition (approximately 52%) of the carbonyl to metallic Ru, as suggested by the difference in the molecular weight of the vaporizing species of 107.58 g/mol compared to the actual value of 639.33 g/mol. The total vapor pressures of these three carbonyls, the average molecular weights of the effusing gases, equilibrium constants for the vaporization reactions, their enthalpies, entropies, and Gibbs energies have been determined.